Electric power suppliers or so-called electric utilities charge higher rates for both summer and winter peak cooling and heating conditions. For example, in warm weather conditions, peak electricity usage is usually in the afternoon hours and in the heating seasons peak electricity usage may be in the early morning hours when heating systems return to normal daytime temperature settings and electric water heaters, for example, are subject to above-normal usage. So-called thermal energy storage systems have been developed for minimizing the use of electrical energy during peak periods. U.S. Pat. Nos. 5,211,029 (to Uselton, et al), issued May 18, 1993 and 5,307,642 (to Dean), issued May 3, 1994, assigned to the assignee of the present invention, and U.S. Pat. No. 5,255,526 (to Fischer) issued Oct. 26, 1993 describe air conditioning systems which utilize a thermal energy storage tank having a phase change material, such as water, disposed therein. During off-peak electricity usage periods, refrigerant is circulated through a heat exchanger in the storage tank to produce ice, and during peak electricity usage periods, refrigerant is circulated between the storage tank and an indoor heat exchanger coil or evaporator by a low-power consuming pump to provide the requisite cooling effect. Thermal energy storage systems may also be used for heating, as shown in U.S. Pat. No. 4,645,908 (to Jones). So-called load leveling systems provide for simultaneous operation of a thermal energy storage unit and a vapor compression refrigerant circuit, as shown in U.S. Pat. No. 4,916,916 (to Fischer).
However, known types of load leveling systems do not provide for two independent indoor heat exchangers which provide cooling simultaneously from both a thermal energy storage unit and from a vapor compression refrigerant circuit. Still further, known types of load leveling systems do not provide for both heating and cooling by simultaneously operating a thermal energy storage unit and a vapor compression refrigerant circuit with respective separate indoor heat exchangers. It is to these ends that the present invention has been developed.